This invention relates to vehicle air conditioning systems and, more particularly, to a vehicle air conditioning system that performs cooling and heating, and a compressor.
In order to solve environmental problems, it has been proposed to employ a substitute for fluorocarbon in vehicle air conditioning systems. For example, carbon dioxide may be employed as a refrigerant to achieve cooling or heating. In addition, there is a need for a small air conditioning system.
Piston type compressors have been widely used in automotive air conditioning systems. Such compressors have a dead volume relative to the volume of the piston stroke, and refrigerant remaining in the dead volume is subjected to re-compression, which reduces the volumetric efficiency. The dead volume tends to increase as the capacity of the compressor decreases and, consequently, it is difficult to provide a small compressor that is efficient.
Further, in order to achieve cooling and heating, the compressor is required to have a compression ratio that varies in a considerably wide range. Under a circumstance in which a high compression ratio is required and the intake pressure is low, such as the beginning of the winter season, that is, when the intake refrigerant has in low density, the power per unit of exhaust volume, or the heating capacity, decreases and the compressor must be operated at a high rotational speed. To increase the air heating performance without increasing the rotational speed of the electric motor, the exhaust volume of the compressor must be increased. To increase the rotational speed of the electric motor, it is required to employ an electric motor having a high rotational speed. To increase the exhaust volume of the compressor, it is required to employ an electric motor that has a large output torque and a high performance inverter unit. This increases the size of the compressor and the manufacturing cost.
It is an object of the present invention to provide a vehicle air conditioning system that is compact, highly efficient for cooling and heating, and low in cost.
To achieve the above and other objects, in a first aspect, the present invention is an air conditioning apparatus used for selectively heating and cooling a passenger compartment of a vehicle.
The air conditioning apparatus includes a compressor, a cooling circuit and a heating circuit.
The compressor includes a suction chamber into which refrigerant is drawn from outside the compressor, a discharge chamber for discharging refrigerant from the compressor, a first compression chamber, in which a first stage of compression is performed, a second compression chamber, in which a second stage of compression is performed, wherein the second stage is subsequent to the first stage, an intermediate chamber for connecting the first compression chamber to the second compression chamber, such that refrigerant discharged from the first compression chamber is led to the second compression chamber by the intermediate chamber. A cooling circuit is connected to the compressor, wherein the cooling circuit is used for cooling the passenger compartment. A heating circuit is connected to the compressor, wherein the heating circuit is used for heating the passenger compartment.
To achieve the above and other objects, in a second aspect, the present invention is an air conditioning apparatus for a vehicle, wherein the apparatus includes a compressor, an internal heat exchanger, an external heat exchanger and a heat exchanger change-over circuit.
The compressor includes a first cylinder bore, a second cylinder bore, wherein the second cylinder bore is smaller in diameter than the first cylinder bore, a first piston located in the first cylinder bore, a second piston located in the second cylinder bore, an intermediate chamber connecting the first and second cylinder bores to one another, an intake chamber connected to the first cylinder bore, an exhaust chamber connected to the second cylinder bore, a drive mechanism for driving the first and second pistons, a first intake valve for conducting refrigerant from the intake chamber to the first cylinder bore, a first discharge valve for conducting refrigerant from the first cylinder bore to the intermediate chamber, a second intake valve for conducting refrigerant from the intermediate chamber to the second cylinder bore, a second discharge valve for conducting refrigerant from the second cylinder bore to the exhaust chamber.
The internal heat exchanger locates in a passenger compartment of the vehicle, wherein the internal heat exchanger has first and second ends, an external heat exchanger located outside the passenger compartment, wherein the external heat exchanger has first and second ends.
The heat exchanger change-over circuit includes a cooling passage, by which the intake chamber of the compressor is connected to the first end of the internal heat exchanger and by which the exhaust chamber is connected to the first end of the external heat exchanger and a heating passage, by which the exhaust chamber of the compressor is connected to the first end of the internal heat exchanger and by which the intake chamber is connected to the first end of the external heat exchanger, wherein the cooling passage is blocked and the heating passage is open during a heating operation, and the heating passage is blocked and the cooling passage is open during a cooling operation.
The expansion valve change-over circuit includes a heating expansion passage to expand refrigerant flowing from the internal heat exchanger and a cooling expansion passage to expand refrigerant flowing from the external heat exchanger, wherein the heating expansion passage is open and the cooling expansion passage is closed during the heating operation, and the cooling expansion passage is open and the heating expansion passage is closed during the cooling operation.